Technical Field
The present invention relates to Extreme Ultraviolet (EUV) pellicle fabrication, and more particularly to drying EUV pellicles during EUV pellicle fabrication.
Description of the Related Art
During semiconductor wafer fabrication, extreme ultraviolet (EUV) light may be employed in, for example, a lithographic process to enable transfer of very small patterns (e.g., nanometer-scale patterns) from a mask to a semiconductor wafer. In EUV lithography, a pattern formed on an EUV lithographic mask (e.g., EUV reticle) may be transferred to a semiconductor wafer by reflecting EUV light off of portions of a reflective surface. A pellicle can be placed in front of the mask to, for example, avoid contamination of the mask and to prevent unwanted particles from reaching the mask surface, which may enable avoidance of alteration of the pattern to be transferred by the mask.
In the case of EUV mask technology, pellicles are conventionally very thin (e.g., ˜100 nm or less), therefore managing the mechanical stability of the ultra-thin pellicle membrane in the presence of outside forces (e.g., capillary force, vibrations, etc.) during fabrication is challenging, especially given the large surface area with respect to the thickness of an EUV pellicle. Among the plurality of forces which may be exerted on an EUV pellicle surface, a comparatively difficult force to overcome is the presence of a capillary force during the withdrawal of the membrane from a rinse bath (e.g., de-ionized water (DI H2O)) for drying of the pellicle. Such capillary force is operative at the liquid-gas-solid boundary on both sides of the partially immersed membrane, and may result in a downward pulling force, which may be described by the Wilhelmy equation (e.g., F=2·γ·l cos θ). Such force (F) may break even small EUV pellicles while the pellicle is being withdrawn from the rinse bath.
Conventional systems and methods that minimize the surface tension (γ) of the drying liquid may force a fluid flow (e.g., Marangoni drying, critical point drying, etc.), and may involve volumetric changes (e.g., freeze drying), or specialty non-volatile chemicals (e.g., rinses including surfactants, Langmuir Blodgett films, etc.). However, no conventional systems or methods can effectively and/or consistently fabricate ultra-thin, large-area EUV pellicles.